With rapid development of semiconductor manufacturing technology, semiconductor devices develop toward higher element density, and higher integration level. Transistors are currently widely used as the most basic semiconductor devices. With increasing element density and integration level of the semiconductor devices, the characteristic sizes of the transistors are getting smaller and smaller. In order to reduce the parasitic capacitance of the transistor gate and improve device speed, gate structures having a high-K gate dielectric layer and a metal gate electrode are introduced into the transistor.
However, problems remain when forming a metal gate electrode on a high-K gate dielectric layer, due to a matching problem of the work function. The work function will directly influence the threshold voltage (Vt) of the device and the performance of the transistor. Thus, a work function layer is introduced into the high-K metal gate structure to adjust threshold voltage of the resultant device.
However, even if a work function layer is introduced in the high-K metal gate structure, the performance of the semiconductor structure in the existing technology still needs to be improved.